In a typical electrophotographic process, an electrophotographic photoreceptor undergoes steps essentially including cleaning, charging, light exposure, developing, and image-transfer. In the electrophotographic process, a cleaning blade is employed to scrape off toner remaining on the surface of an electrostatic latent image carrier such as a photoreceptor. From the viewpoints of plastic deformation and wear resistance, the cleaning blade is generally formed of a thermosetting polyurethane elastomer.
However, when a cleaning blade formed of a polyurethane elastomer is employed, the friction coefficient between the blade member and a photoreceptor drum increases, and delamination of the blade and anomalous sound problematically occur. Also, the driving torque of the photoreceptor drum must be increased in some cases. Furthermore, the edge of the cleaning blade may be wound to a photoreceptor drum or another member, whereby the cleaning blade is stretched or cut, and the edge of the cleaning blade is broken due to wear. These problems become severe particularly when the cleaning blade has low hardness. As a result, the durability of the cleaning blade is impaired.
In order to solve the aforementioned problems, the contact portion of a polyurethane blade has been modified to have high hardness and low friction. In one proposed procedure, a polyurethane blade is impregnated with an isocyanate compound, to thereby induce reaction between the polyurethane and the isocyanate compound, whereby the hardness is enhanced at only the surface or a portion near the surface, and wear of the surface is reduced (see, for example, Patent Documents 1 and 2).
However, in order to attain a target surface hardness, in the blades disclosed in Patent Documents 1 and 2, a polyurethane body must be impregnated with a surface treatment liquid having high isocyanate compound concentration, to thereby form a thick treated surface layer. For forming such a thick treated surface layer, an excess amount of isocyanate is unavoidably applied to the blade surface. Thus, the excess amount of isocyanate must be removed. In contrast, when the thickness of the treated surface layer is reduced, neither a target surface hardness nor low friction can be attained. In this case, wear resistance and delamination resistance cannot be fully attained, which is problematic.
Meanwhile, in order to enhance wear resistance, there has been proposed a blade having a contact portion in which nitrogen concentration continuously increases from the inside thereof to the surface thereof (see, for example, Patent Document 3). However, the blade disclosed in Patent Document 3 has a large difference in nitrogen concentration between the inside and the surface of the contact portion, and the nitrogen concentration is relatively high at the surface of the contact portion. Therefore, similar to the blades disclosed in Patent Documents 1 and 2, a step of removing isocyanate is required. In addition, due to a large difference in nitrogen concentration between the inside and the surface of the contact portion, the flexibility of the blade is lost, to thereby fail to ensure long-term cleaning performance, which is also problematic.
Under such circumstances, there has been proposed a technique in which the amount of an isocyanate compound caused to be present at the contact portion is adjusted to an appropriate level, thereby omitting the isocyanate compound remaining at the surface after impregnation, whereby the hardness of the top surface portion of the contact portion can be effectively elevated, and rubber elasticity can be ensured in a portion near the contact surface (see, Patent Document 4).
However, even when the technique disclosed in Patent Document 4 is employed, when the hardness of the contact portion is sufficiently enhanced, the impregnation amount unavoidably increases. Thus, flexibility in the vicinity of the contact portion is impaired, to thereby cause warpage at the contact portion, and the surface of the contact portion is coated with the remaining surface treatment liquid, which are also problematic. As a result, problematically, the blade body must be wiped after surface treatment or cutting, and consistent surface treatment fails to be attained.